This study aimed to increase UV light exposure and provide enrichment for a captive green sea turtle named Dot. Twice weekly, enrichment objects containing food were placed under Dot's UV lamp and she was observed for 30 minutes. The large enrichment ball was most successful at holding Dot's attention for 30+ minutes as she manipulated it to access the food. While the study was successful in providing enrichment and more UV exposure, modifications could improve the measurement of its effects on Dot's vitamin D levels over time. Continued studies are needed to understand captive sea turtles' needs and contribute to the health of an increasing captive population.

1. UV light effects on captive green sea turtles (Chelonia mydas)
Kaitlyn Pleau, Biology, Zoology
Dr. Rebecca Doyle-Morin, Thesis Advisor
Abstract
Concerns were expressed about the amount and benefits of UV
light exposure a captive, female green sea turtle (Chelonia mydas)
has been receiving at the National Mississippi River Museum and
Aquarium. Being in captivity for nearly three years, it is possible
that the turtle is not receiving an adequate amount of Vitamin D3.
This vitamin is vital to nearly all living forms and contributes to
absorption of calcium which directly relates to carapace and bone
health. Vitamin D3 can be ingested through a UV lamp or food
products. Vitamin D3 is converted upon absorption into an active
form known as serum 25-hydroxyvitamin D. A recent decade-long
study showed that serum 25-hydroxyvitamin D dropped drastically
for indoor-held captive green sea turtles. Although there are no
apparent issues with the sea turtles, scientists believe this will
become a problem in the decades to come as the amount of captive
sea turtles increase. To avoid these issues, a study was created to
combine feeding enrichment with an increase of UV light by a
consecutive thirty minutes. As part of an internship, three
enrichment objects have been utilized with her normal, daily
feeding to capture her attention and keep her at the surface. With
this increase in surface feeding times, it is hoped that serum 25-
hydroxyvitamin D will increase as years proceed.
Introduction
Vitamin D is constantly recommended to humans to strengthen bones. It is actually just as
important to sea turtles as it is to humans. In sea turtles, vitamin D3 helps with the absorption of
calcium within the body, specifically the intestines (Lutz and Musick 1996). Vitamin D3 is a
form of vitamin D that is absorbed from the sun. The vitamin eventually metabolizes into serum
25-hydroxyvitamin that is the active form of the vitamin (Haussler et. Al 1971). Serum 25-
hydroxyvitamin is essentially how we define the amount of vitamin D within our bodies (Holis
2007). There is much debate on the minimum levels of vitamin D3 required for both humans and
reptiles (Holis 2007). Regardless of the minimum levels, it has been seen in a previous study that
the serum 25-hydroxyvitamin D levels decrease over four times the original amount before

2. 2
captivity (Purgley 2009). The decrease in blood levels begin four to five months after initial
captivity (Purgley 2009). With the uncertainty of the amount of vitamin D required by green sea
turtles, it is important to try to mimic the natural world as closely as possible to eliminate any
possibilities of deficiencies.
The main way green sea turtles absorb vitamin D3 is through UV light. UV light is an invisible
form of light that plays an important role in calcium metabolism through serum 25-
hydroxyvitamin D (Adkins et al. 2003). There are two types of UV light present in nature: UVA
and UVB. UVB is the rays utilized by sea turtles to help with synthesizing of vitamin D3 and
possibly reducing ulcerative dermatitis (Adkins et al. 2003). Green sea turtles are known to
maximize the amount of UV light present for absorption. Specific species of green sea turtles
bask on beaches of unpopulated islands including French Frigate Shoals, HI (Whittow and
Balazs 1982). It was observed that some turtles remained basking for nearly 600 minutes at one
time (Whittow and Balazs 1982). With this amount of basking, it raises questions about exactly
how much vitamin D3 is necessary for a healthy lifestyle.
Certain species of turtles are able to receive their calcium from their diet because they are
primarily carnivorous, but green sea turtles are only omnivorous while juveniles (Purgley 2009,
Arthur et al. 2008). During their adult years they are nearly completely herbaceous, obviously
resulting in little to no calcium intake from their diet (Arthur et al. 2008). This proves how
imperative UV light is to sea turtles.
In light of the recent environmental issues that are affecting the oceans, the likelihood of more
sea turtles coming into captivity is high (Purgley 2009). Because UV light is so prevalent in their
lives, it is important to allow them to receive the correct amount even while indoors. This study
was created in order to maximize the amount of vitamin D received by the green sea turtle
residing at the National Mississippi River Museum and Aquarium (NMRMA), via her UV lamp
located above her tank. Being an organism who has received little enrichment throughout her
stay at NMRMA, it was a priority to incorporate some natural behavior to encourage some kind
of basking. Information was recorded for seven weeks, but should be continued as this is an
ongoing issue that will affect the turtle many years from now.
Methods
Study Subject
A captive green sea turtle was used as the test subject in this experiment. The green sea turtle,
Dot, has been in captivity since July 2013 and has been on exhibit at NMRMA in Dubuque, IA
since June 2014. Dot was found stranded on Little Cumberland Island, GA where she was
believe to be struck by a boat. She was taken to the Georgia Sea Turtle Center on Jekyll Island,
GA where she was treated for a mid-caudal carapace fracture. The injury caused a buildup of gas
within her and paralysis of both hind flippers. Since arriving at NMRMA, she has spent a great

3. 3
amount of time with a weighted pack epoxied on the hind end of her carapace to level out the gas
build up and allow for level swimming. During the study, Dot does not have the pack on due to
her ability to counter the floating back end. Before this experiment, Dot has experienced little to
no enrichment training but she has been target trained by her primary keeper with a red PVC
pipe for a target and food rewards.
Enrichment Objects
Three enrichment objects were chosen for the study. Each offers a new and unique experience
for her. All the objects were chosen to capture Dot’s attention and hold it for thirty minutes; but
also to simplify the target training enough for the full-time aquarist to continue the study past the
original trials. The first, a small enrichment ball, is bowling ball sized, hollow and has two
softball sized holes in the sides. This was chosen as its size did not intimidate, in theory, and is
large enough to hold a full feeding. The second is a large enrichment ball, roughly the size of a
large beach ball and significantly heavier, that has approximately fifteen golf ball sized holes
around the sides. It provides a more challenging object for Dot to experience. The last, a PVC
pipe ring in the shape of a hexagon, is four feet in diameter and designed to hold the floating
food within the boundary.
Placement of Objects in Exhibit
Crucial to the experiment was object placement. In one area of the tank, a UV lamp that is
suspended from the ceiling dangles over a portion of the water. Under the lamp, the water that
enters the tank creates a circulating effect on the water’s surface. The researcher always places
each object directly under the light to allow the object to flow in the circulating water throughout
the duration of the trial.
Trials
Trials were held twice a week for a span of seven weeks. Each trial lasted thirty minutes with the
enrichment objects randomly selected each time to ensure Dot was not accustomed to a schedule.
A rotation of half and full feedings loaded into the object is used depending on the day.
Enrichment Loading
A variety of vegetables are used for Dot’s feedings. She prefers full heads of lettuce, bok choy,
carrots, celery and her favorite, red bell peppers. Cucumbers, butternut squash and zucchini were
not chosen because she will not eat them. Because of timing on certain days, only half her
normal feeding was used for the study so she could be fed in the afternoon for an educational
event.
Analysis
Scientific tests were not conducted to measure her reaction to the ball. Instead, a journal was kept
with detailed notes of her reactions towards the enrichment object and the amount of time needed
to complete the trial. Recordings on minor details regarding half or full feedings, time of day,

4. 4
whether she had to be woken from her mid-morning nap, were all recorded and considered when
reviewing the successfulness of the day. Blood tests were not available before or after the trials
to compare vitamin and other nutrient levels within her. To further this study, blood tests should
be conducted to create a more effective and measurable outcome.
Results
Small Enrichment Ball
The small enrichment ball was used for the very first trial. It was loaded with a full feeding and
placed into the water under the light. Dot approached the object without hesitation and began to
eat from it right away. After two minutes of nibbling, Dot darted away and would only hesitantly
come back to nip at the ball for the next five minutes. After the nipping subsided, she came back
to the ball and continued to eat from it. After eating some of the buoyant lettuce, the ball sank to
the bottom of the tank. Although it did not meet the main goal of the study, UV exposure, it was
a successful trial in terms of strictly enrichment. Dot was engaged for thirty minutes and actively
interacting with the object. This trial did also require Dot to expend a great amount of energy
because of her gas buildup; she was unable to remain parallel to the ground so she constantly
bobbed up and down towards the sunken ball. She constantly pumped her flippers hard for the
duration of the trial to reach the ball which was located at the bottom of the tank.
PVC Pipe Ring
Throughout the rest of the trials a rotation between the PVC pipe ring and the large enrichment
ball were used. The PVC pipe ring resulted in both positive and negative qualities. It did manage
to stay within the study area the majority of the time and could hold either a full or half feeding.
It did not, however, meet the time requirement needed for benefit. The object seemed too easy
for Dot and did not challenge her in a way that would maximize her exposure to UV rays. Also,
due to Dot’s hind end floating more elevated than the rest of her body, as she would swim
underneath to reach the food, the pipe would become lodged on her back, allowing the food to
escape from the ring. The ring needed constant reloading which interrupted the test in progress.
After Dot consumed the food, she did interact with the ring by pecking at it during the final
minutes it remained in the water to conclude the trial.
Large Enrichment Ball
Upon analyzing the results, the large enrichment ball was the most successful object throughout
the trials. Like the PVC pipe ring, it resulted in both positives and negatives. The large ball
always used the full thirty minutes, if not more, regardless of whether it was a full or half
feeding. Having the food surround the large ball caused Dot to rotate the ball with her flipper to
retrieve all of the food. At the beginning of the trial, the ball remained in the study area. As Dot
would attempt to pull the food out of the ball, she pushed against it with her fore flipper which
caused the ball to float out of the study site. The ball then would float around the entire tank for
the rest of the trial thereby decreasing her exposure to the UV rays.

5. 5
Discussion
The purpose of this study was to increase the amount of UV light exposure Dot was exposed to
while providing her with enrichment. It was successful in both cases as her twice a week trials
resulted in her staying at the surface near her lamp more than previously. It also added another
stimulant into her enclosure which encourages natural behaviors. The two main objectives of this
study are very important to the health of green sea turtles. With an adjustment to some of the
details of the study, benefits for continuing the study strongly exist. The successfulness of the
face-value of this study should be capitalized to further stimulate Dot.
There is not much literature available to support this study. There is, however, plenty of
acknowledgements to the issue studied above and the recognition of needing more emphasis on
the subject. Even with such little information about captive green sea turtle’s serum 25-
hydroxyvitamin D levels, there is even less known about wild turtles. It is difficult to use
literature, at this point in time, to support the study and the findings. As studies occur, this
information will be become more valuable. Data collection to submit to future studies and
literature should begin. With the lack of literature, it does create conflict in determining exact
details when constructing a study. The exact amount of time necessary to absorb the correct
amount of vitamin D3 is unknown which causes variations in different studies. Not knowing the
exact amount of time can lead to positive and negative results. It can cause variation in current
studies so information is more broad and numerous but it could result in unusable data.
Contact with an established long-term study on this same issue should be made to be able to
contribute to the data pool already collected. Without doing this early on, the data collected may
not be usable for the study due to minor issues. Because of Dot’s injury, it may be difficult to get
accurate blood levels. The injury may affect these and cause the serum 25-hydroxyvitamin D
levels to be skewed. This needs to be addressed immediately to resolve the question.
Although there is no numerical data to compare, the point of the study was to create a baseline
for enrichment. It should be continued and its ongoing data collection can contribute to current
studies. In regards to enrichment, this was a very successful study. Dot was accepting of all
methods of enrichment and genuinely seemed excited about the additional difficulty added to
feedings. It was unexpected that little to no conditioning was necessary during the introductory
period of the enrichment objects. She was fully expected to have great amounts of hesitation and
discomfort shown towards the objects. Because Dot was target trained and is comfortable with
diver’s entering the tank for weekly cleanings, this may have helped with the introductory
period.
This study should be continued for three reasons: enrichment, vitamin D3 absorption and future
studies. No harms were detected during this study as reasons to discontinue this project, only

6. 6
benefits for Dot and other turtles held in captivity. The study techniques should be modified,
however, to create a more efficient method of enrichment and a method of calculating data.
Blood work should be taken at the beginning of the project and tested every six months to track
the path of the levels. Visuals should also be noted of Dot’s hind scutes to see if any
improvement is seen regarding her carapace. The main technical flaw that should be addressed
would be the actual enrichment object. Each of the objects offered good qualities to the study,
but none were completely appropriate. To continue the study, a new object should be created and
introduced to maximize the UV exposure and the enrichment aspects. An enrichment ball should
be constructed with the amount of holes present in the large enrichment ball. The ball size itself
should be favoring the smaller ball than the larger one but still be in between the two sizes.
Surrounding the enrichment ball, should be a PVC pipe ring that encircles the area where the
light touches the water. It should be large enough so Dot has enough room to move around in the
ring with the ball but also compact enough so the aquarists can easily set up, break down and
store the items. This would create the perfect enrichment object for this study. The trials should
also occur on a more consistent schedule. This information should be obtained from a long-term
study previously mentioned.
In light of recent detrimental events, the possibility that the environment will not be suitable for
green sea turtles to remain in their natural habitat remains a threat. The possibility of an increase
of captive green sea turtles is very high and institutions need to be able to supply them with an
enclosure that represents their natural habitat as closely as possible. As stated before, UV light
seems to play a huge role in their lives regardless of knowing the full benefits. It remains
important to continue this study with all captive green sea turtles to compare blood levels with
other turtles around the world for the next few decades. A study including blood levels of wild
green sea turtles would offer a strong comparison to the captive turtles. This is an issue that will
not affect these turtles now but instead in a few decades. A variety of health issues due to the
vitamin D3 deficiency seems likely and it would benefit the turtles to avoid these issues by
creating enclosures that mimic natural habitats.
Literature Cited
Adkins, E., T. Driggers, G. Ferguson, W. Gehrmann, Z. Gyimesi, E. May, M. Ogle, and T.
Owens. 2003. Ultraviolet Light and Reptiles, Amphibians: Roundtable. Journal of Herpetological
Medicine and Surgery 13(4): 27-37.
Arthur, K.E., M.C. Boyle, C.J. Limpus. 2008. Ontogenetic changes in diet and habitat use in
green sea turtle (Chelonia mydas) life history. Marine Ecology Progress Series 362: 303-311.
George, Robert H. 1996. Health Problems and Diseases of Sea Turtles. Pg. 363-386 in P.L. Lutz
and J.A. Musick, editors. The biology of sea turtles. CRC Press, Boca Raton, Florida, USA.

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Haussler, M.R., D.W. Boyce, E.T. Littledike, and H. Rasmussen. 1971. A Rapidly Acting
Metabolite of Vitamin D3. Proceedings of the National Academy of Science 68(1): 177-181.
Hollis, B.W., C.L. Wagner, M.K. Drezner, N.C. Binkley. 2007. Circulating Vitamin D3 and 25-
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Status. J Steroid Biochem Mol Biol 103(3-5): 631-634.
Purgley, H., J. Jewell, J.E. Deacon, R.M. Winokur, and V.M. Tripoli. 2009. Vitamin D3 in
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